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• Ffmpeg inaccurate cut duration with ts [duplicate]

  30 juillet 2020, par Lemon Sky

  I need to accurately seek and cut a video. Some online sources say put -ss in front or after the source. The result is the same for me. In the examples below, the start time is accurate but the duration is not accurate.

  


  ffmpeg -y -ss 00:00:05 -t 00:00:05 -i http://tyberis.com/output.ts 5s.wav
ffprobe 5s.wav

Duration: 00:00:04.74

ffmpeg -y -i http://tyberis.com/output.ts -ss 00:00:05 -t 00:00:05 5s.wav
ffprobe 5s.wav

Duration: 00:00:04.74


  


  Sometimes the starting point is not accurate but the duration is. This is clearly audible by cutting the ts file and cutting an uncompressed wav file, and listening to both.

  


  ffmpeg -y -i http://tyberis.com/output.ts -ss 00:00:15 -t 00:00:05 5s.wav

ffmpeg -y -i http://tyberis.com/output.wav -ss 00:00:15 -t 00:00:05 5s-reference.wav


  


  What fixes the starting time is if I use an m3u8 file that contains the byte offset for every keyframe AND I put the -ss option in front of the source file (if I put it after the source, the start time is inaccurate but the duration is accurate) :

  


  ffmpeg -y -ss 00:00:15 -t 00:00:05 -i http://tyberis.com/output.m3u8 5s.wav


  


  This fixes the start time but the duration is at the location that I would get had I used no m3u8 file (duration is just 4.47s).

  


  It seems different timestamps are involved, and sometimes one or the other gets used.

  


  The ts file was generated by capturing a UDP stream and storing it with ffmpeg and -codec:v copy.

  


  Is ffmpeg broken, or the ts file ? How do I work around this issue or fix the ts file ? What I realize is that the video starts later than the audio, probably because the video does not start with a keyframe. Can I get ffmpeg to start the -codec:v copy after the first keyframe ? What I also notice is that using ffprobe reports "start : 1.400000". Can I force it to start at 0 ?

  


  Any hints would be appreciated.

  


  I tried both ffmpeg 4.3.1 and ffmpeg git-2020-07-24-21442a8.

  


• Ffmpeg inaccurate cutting with ts and m3u8 files despite resamping audio filter

  31 juillet 2020, par Lemon Sky

  I need to accurately seek and cut a video. Some online sources say put -ss in front or after the source. The result is the same for me. In the examples below, the start time is accurate but the duration is not accurate.

  


  ffmpeg -y -ss 00:00:05 -t 00:00:05 -i output.ts 5s.wav
ffprobe 5s.wav

Duration: 00:00:04.74

ffmpeg -y -i output.ts -ss 00:00:05 -t 00:00:05 5s.wav
ffprobe 5s.wav

Duration: 00:00:04.74


  


  Sometimes the starting point is not accurate but the duration is. This is clearly audible by cutting the ts file and cutting an uncompressed wav file, and listening to both.

  


  ffmpeg -y -i output.ts -ss 00:00:15 -t 00:00:05 5s.wav

ffmpeg -y -i output.wav -ss 00:00:15 -t 00:00:05 5s-reference.wav


  


  What fixes the starting time is if I use an m3u8 file that contains the byte offset for every keyframe AND I put the -ss option in front of the source file (if I put it after the source, the start time is inaccurate but the duration is accurate) :

  


  ffmpeg -y -ss 00:00:15 -t 00:00:05 -i output.m3u8 5s.wav


  


  This fixes the start time but the duration is at the location that I would get had I used no m3u8 file (duration is just 4.47s).

  


  It seems different timestamps are involved, and sometimes one or the other gets used.

  


  The ts file was generated by capturing a UDP stream and storing it with ffmpeg and -codec:v copy.

  


  Is ffmpeg broken, or the ts file ? How do I work around this issue or fix the ts file ? What I realize is that the video starts later than the audio, probably because the video does not start with a keyframe. Can I get ffmpeg to start the -codec:v copy after the first keyframe ? What I also notice is that using ffprobe reports "start : 1.400000". Can I force it to start at 0 ?

  


  Any hints would be appreciated.

  


  I tried both ffmpeg 4.3.1 and ffmpeg git-2020-07-24-21442a8.

  


  The output.* files were generated as follows. The statement "af aresample=async=1" should fill missing audio according to Duration of source video and subtracted audio are different. Adding this statement makes no difference in terms of accuracy or duration. The question is not a duplicate.

  


  ffmpeg -i udp://example:port ^
-af aresample=async=1 ^
-codec:v copy ^
-codec:a aac -ac 2 -ar 44100 -b:a 160k ^
-hls_time 4 -hls_flags single_file -hls_list_size 0 -hls_segment_filename output.ts -hls_segment_type mpegts output.m3u8 ^
-codec:a pcm_s16le -bitexact -ar 11025 -ac 1 output.wav


  


• How to write bmp-frames into avi container using ffmpeg ?

  2 septembre 2020, par Alexey Matal

  I have a sequence of bmp-files, format : 8bpp. How to write this sequence to avi-file using ffmpeg ?

  


  In other words : I need create "AVI-container with BMP-codec".
if specifically then : what is the codec and pixel-format I need to choose of ffmpeg scope ?

  


  In ffmpeg examples, in context initialisation present next code :

  


  c->bit_rate = 400000;
/* resolution must be a multiple of two */
c->width = 352;
c->height = 288;
/* frames per second */
c->time_base = (AVRational){1, 25};
c->framerate = (AVRational){25, 1};

/* emit one intra frame every ten frames
 * check frame pict_type before passing frame
 * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
 * then gop_size is ignored and the output of encoder
 * will always be I frame irrespective to gop_size
 */
c->gop_size = 10;
c->max_b_frames = 1;
c->pix_fmt = AV_PIX_FMT_YUV420P;


  


  What is the bit_rate, gop_size, max_b_frames (what ? in BMP ?) parameters ?

  


  Thanks !

  


  ps this functionality is a part of big legacy-project. AVI-file in past wrote manually. I don't want write it manually, please help :)